From I first encountered rules surrounding this, it has always been seen as a workaround to create the incentives to change sexism elsewhere.

E.g if boards are required to put women in place, it creates an organizational incentive to improve the conditions so more women gets the training and promotions and mentoring that makes then suitable for those board positions, and also takes away an ability to avoid hiring qualified women.

I don't know if anyone that see those rules as desirable in and of themselves.